Printed circuit board assemblies are comprised of a printed circuit board and electronic components which are positioned on and electrically connected to circuitry formed on the printed circuit board. Printed circuit boards as manufactured have a continuous foil of conductive material adhered to at least one of the surfaces of a core of a dielectric material. The continuous conductive foil on the printed circuit board is thereafter patterned using conventional techniques to remove portions of the conductive material so as to form a predetermined circuit pattern. Holes are punched or drilled through the circuit boards at predetermined locations with the holes generally being in registration with selected solder pads formed as part of the circuit pattern etched in the conductive foil. Electronic components are then mounted at predetermined locations on the printed circuit board. The electronic components are temporarily secured in position until they can be permanently soldered in place.
The type of electronic components which have heretofore been generally employed are referred to as leaded components. The electronic elements of the leaded component are encapsulated in a dielectric casing with leads extending from the casing for connecting the component to the circuitry of a printed circuit board. The leads can be in various forms such as wires, pins, legs or the like. When manufacturing printed circuit board assemblies using leaded components, the components are mounted on the surface of the board opposite the side on which the circuitry is normally formed and the leads of the components are inserted through the preformed holes in the printed circuit board. If gravity is not sufficient to hold the leaded components in place, a weight can be placed on the leaded components; the leads of the components can be bent to prevent movement of the components or an adhesive can be used to hold the leaded components in place. After the leaded components are inserted into the printed circuit boards, the leads thereof can be mass soldered to the circuitry of the printed circuit board by methods such as dip soldering or wave soldering. Mass soldering of leaded components is a relatively straight forward process in that the leaded components are mounted on the top surface of the printed circuit board, which does not enter the solder bath, while the bottom surface having the circuitry defined thereon with the leads in registration with solder pads is immersed in the solder bath for soldering.
Recently, there has been developed a new class of electronic components referred to as leadless components. The leadless components differ from the leaded components in that the electronic elements thereof are encased in a dielectric material and then, instead of having leads extend from the components, have exposed metal electrodes at the terminals. The leadless components are generally made in a right parallelpiped configuration and are designed to be directly soldered to soldered pads on the bottom surface of a printed circuit board.
A very significant problem which has been encountered when manufacturing printed circuit boards which had leadless components, is that it is often difficult to adequately secure leadless components to the printed circuit board so they remain in position until the soldering of the leadless components to the circuitry is completed.
The method heretofore most commonly used for securing leadless components to printed circuit boards prior to and during soldering has been to apply a small amount of an adhesive to the positions on the printed circuit board where the leadless components are to be mounted and then place the leadless components in contact with the adhesive so as to bond the leadless components to the surface of the printed circuit board. This technique, however, has met with at best limited success. The adhesives generally form a satisfactory bond with the dielectric material used to encapsulate the leadless components but the bond with the printed circuit board is often at best marginal. The poor bonding of the leadless components to surface of the printed circuit board is believed to be caused by a variety of factors such as the dielectric material of the board not being wet out by the adhesive; the smooth surface of the printed circuit board inhibiting a strong mechanical bond from forming between the leadless components and the board; contaminates such as flux on the surface of the boards and the poor bonding character of certain dielectric material used to make the printed circuit boards. Because of the problem of displacement of leadless components using the prior art methods, it has been necessary to individually examine each printed circuit board assembly after mass soldering and to replace the missing components in a hand soldering operation. The excessive inspection required is highly undesirable and hand soldering is extremely expensive and more prone to cause soldering defects than mass soldering.
Accordingly, what would be highly advantageous would be an improved method for securing leadless components to printed circuit boards so as to prevent or substantially reduce the loss or displacement of leadless components from printed circuit boards prior to and during soldering of the circuit board assemblies.